The present invention relates to liquid delivery systems and, in particular, it concerns an apparatus and method for measuring the timing and quantity of doses delivered by a pen-injector type drug delivery device and/or monitoring the quantity of drug remaining in the device.
In the field of liquid delivery devices, and particularly pen injectors, there is a need to provide the user with reliable information regarding previously administered doses of a liquid drug.
Various attempts have been made to add functionality to pen injectors by providing a smart cap. By way of example, U.S. Pat. No. 8,743,662, coassigned with the present invention, discloses a smart cap for a pen injector which monitors the time which has elapsed since a previous use of the pen injector.
Other smart cap devices have attempted to measure the quantity of a drug dose dispensed. One example of such a device is U.S. Pat. No. 8,817,258. This device requires an extensive array of optical sensors extending along the cap.